The invention relates to a local communication bus system comprising first and second apparatuses connected for the exchange of messages to a serial data channel, and to apparatuses for use in such a system. The invention relates in particular, but not exclusively, to a system of domestic audio and video apparatuses interconnected by a serial data channel bus for the exchange of control messages.
A known serial data channel of this type is provided by the Domestic Digital Bus (D2B), standardised by the International Electotechnical Commission (IEC), Geneva. The name D2B is a trademark of Philips Electronics NV. Examples of apparatuses including D2B interfaces are Philips' model 2070 television receiver and model VR6590 video cassette recorder (VCR) previously available in Europe. Such a data channel has many applications, and it is desired that a standardised set of `application protocols` be developed, in addition to the basic communication protocols defined by the IEC, and that these protocols should be adhered to by many manufacturers of consumer apparatus. In particular, the use of such protocols can bring enhanced functionality and ease of use to the great variety of consumer electronic apparatuses available today and in the future, with true inter-brand compatibility.
The known apparatuses, for example, provide for integrated on-screen display facilities, so that a user controlling the VCR can receive information about the progress of VCR operations via the television screen. Such a feature is described in more detail in our copending European patent application EP-0 505 006-A2 (PHQ91010), not published at the priority date of the present application. There is a desire to integrate further the operation of the apparatuses of the system, for example to allow the user to have dialogue with an apparatus which itseIf has inadequate user input/output facilities. One example would be to provide menu driven control of an apparatus which itself has no means for displaying a menu, and/or no means for relating a displayed menu to input received from the user. While this is clearly possible in theory, there is an overriding cost requirement to minimise the amount of information that one apparatus must `know` about the other apparatuses of the system. Furthermore, it is desirable for the user dialogue functions to integrate all apparatuses of the system, rather than being restricted to the control of only one apparatus in a given session.
A prior system for remote menu display has been proposed in the "Specification of the interface between a Conditional Access Sub-System implemented as an integrated circuit card and a MAC-receiver", released by Norwegian Telecom in July 1990. While this proposal allows the IC card ("Smart card") to display a menu and receive a user selection, this depends strictly on the availability of specific marked keys on the receiver handset. The smart card is furthermore required to receive information of all user control signals (for example "volume up"), whether or not they relate to its own user dialogue. There is also no facility to integrate the user interface of many apertures of the system.
Software interfaces for user dialogue within a single computer-controlled apparatus are also known, for example in the Apple Macintosh Computer, and the Gem User Interface Toolkit for Atari computers.